Self-sealing of fractures in indurated claystones measured by water and gas flow

Self-sealing of fractures in the indurated Callovo-Oxfordian(COX)and Opalinus(OPA)claystones,which are considered as host rocks for disposal of radioactive waste,was investigated on artificially fractured samples.The samples were extracted from four lithological facies relatively rich in clay mineral,carbonate and quartz,respectively.The self-sealing of fractures was measured by fracture closure,water permeability variation,gas penetration,and recovery of gas-induced pathways.Most of the fractured samples exhibited a dramatic reduction inwater permeability to low levels that is close to that of intact rock,depending on their mineralogical composition,fracture intensity,confining stress,and load duration.The self-sealing capacity of the clay-rich samples is higher than that of the carbonate-rich and sandy ones.Significant effects of sample size and fracture intensity were identified.The sealed fractures become gas-tight for certain in-jection pressures.However,the measured gas breakthrough pressures are still lower than the confining stresses.The gas-induced pathways can recover when contacting water.These important findings imply that fractures in such indurated claystones can effectively recover to hinder water transport but allow gas release under relatively low pressures without compromising the rock integrity.

Breakthrough of shallow shale gas exploration in Taiyang anticline area and its significance for resource development in Zhaotong, Yunnan Province, China

Based on exploration and development results and evaluation of marine shale gas in South China in the past ten years, in view of the features of "high maturity, strong tectonic reformation and high shear stress" of the shale in Zhaotong exploration zone in the Yunnan and Guizhou Plateau, as well as the key issues of long time diffusion and leakage of shallow shale gas, and the preservation conditions, the factors controlling shallow shale gas sweet spot and key zone selection evaluation technology of shale gas are investigated. From 2017 to 2018, the first significant exploration breakthrough was made in the Taiyang anticline at a buried depth of 700 to 2 000 m, discovering large-scale proved geological reserves of shallow shale gas. By examining the accumulation conditions and sweet spot control factors of the shallow shale gas in this area, it is found that the accumulation and productivity potential of shale gas in the mountainous area with complex structure outside basin are controlled by five factors:(1) The gas-rich area has weak tectonic reformation and good preservation conditions on the whole, taking on typical anticline trap occurrence mode.(2) The gas-rich area is in over-pressure state and high in shale gas content.(3) The gas-rich area has high quality shale and thus superior source rock condition.(4) The gas-rich area has high quality reservoirs dominated by class I.(5) The shale gas reservoir in the gas-rich area has high content of brittle minerals and small difference between maximum and minimum horizontal stresses which are conducive to hydraulic fracturing. The innovative practice and core technologies formed during the exploration and production capacity construction of shallow shale gas in the Zhaotong demonstration zone have great reference significance for shallow shale gas exploration and development in other areas.

Technical Breakthrough for Fracturing Gas Reservoir

ＴｅｃｈｎｉｃａｌＢｒｅａｋｔｈｒｏｕｇｈｆｏｒＦｒａｃｔｕｒｉｎｇＧａｓＲｅｓｅｒｖｏｉｒ￥ＧａｏＤａｋａｎｇ，ＤｅｐｕｔｙｇｅｎｅｒａｌｍａｎａｇｅｒｏｆＨｕａｍｅｉ－ＨａｌｌｉｂｕｒｔｏｎＣｏ．，ＬｔｄＨｕａｍｅｉ－ＨａｌｌｉｂｕｒｔｏｎＰｅｔ...

Influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based dechlorination agent

Using fixed-bed reaction method and changing the gas composition and dust content,the influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based antichlor was studied.It was found that,when the content of CO2 in blast furnace top gas increased,the dechlorination efficiency was getting worse obviously;when the contents of CO and N2 increased,the dechlorination efficiency was getting better to a certain extent;when the content of H2 changed,the dechlorination efficiency got no significant change;as the content of dust increased,the dechlorination efficiency got better obviously when the content was less than 15 g/m3,but it would be got worse quickly when the content was more than 20 g/m3,and the best content was 15–20 g/m3;the suitable site of the process of dechlorination was after gravity dust collector and before bag dust collector.

WATER BREAKTHROUGH SIMULATION IN NATURALLY FRACTURED GAS RESERVOIRS WITH WATER DRIVE

In the fractured water drive reservoirs of China, because of the complex geological conditions, almost all the active water invasions appear to be water breakthrough along fractures, especially along macrofraetures. These seal the path of gas flow, thus the remaining gas in the pores mixes into water, and leads to gas-water interactive distribution in the fractured gas reservoir. These complicated fraetured systems usually generate some abnormal flowing phenomena such as the crestal well produces water while the downdip well in the same gas reservoir produces gas, or the same gas well produces water intermittently. It is very difficult to explain these phenomena using existing fracture models because of their simple handling macrofractures without considering nonlinear flowing in the macrofractures and the low permeability matrix. Therefore, a nonlinear combined-flowing multimedia simulation model was successfully developed in this paper by introducing the equations of macrofractures and considering nonlinear flow in the macrofractures and the matrix. This model was then applied to actual fractured bottom water gas fields. Sensitivity studies of gas produetion by water drainage in fractured gas reservoirs were completed and the effect of different water drainage intensity and ways on actual gas production using this model were calculated. This model has been extensively used to predict the production performance in various fractured gas fields and proven to be reliable.

A Hierarchically Porous Metal-Organic Framework from Semirigid Ligand for Gas Adsorption

Hierarchically porous materials play an important role in facilitating mass transport and improving efficiency of adsorption and separation processes. In this paper, a new strategy is proposed to realize a hierarchically porous metal-organic framework （[Cu2（OH）（L）]＇（DMF）0.8 （FJU-11, H3L=3,5-（4-carboxybenzyloxy）benzoic acid, DMF= N,N-dimethylformamide） via using semi-rigid multi-carboxylic acids. Interestingly, FJU-11 possesses the large adsorption capacities and small isosteric heats toward CO2. The column breakthrough experiment for FJU-11 highlights its potential application in the separation of the flue gas.

A Study on the Transport Process in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells

Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures.It is found that the relationship between the breakthrough pressure and the temperature is nearly linear(i.e.the pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment.The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.

Pore structure evolution of mudstone caprock under cyclic load-unload and its influence on breakthrough pressure

The pore structure of caprock plays an important role in underground gas storage security, as it significantly influences the sealing capacity of caprock. However, the pore structure evolution of caprock with the cyclic stress perturbations triggered by the cyclic gas injection or extraction remains unclear. In this study, the pore structure changes of mudstone caprock under cyclic loading and unloading were obtained by the nuclear magnetic resonance (NMR) tests system, then the influence of the changes on the breakthrough pressure of caprock was discussed. The results indicated that the pore structure changes are depending on the stress loading-unloading path and stress level. In the first cyclic, at the loading stage, with the increase of confining stress, the NMR T2 spectrum curve moved to the left, the NMR signal amplitude of the first peak increased, while the amplitude of the second peak decreased gradually. This indicated that the larger pores of mudstone are compressed and transformed into smaller pores, then the number of macropores decreased and the number of micro- and mesopores increased. For a certain loading-unloading cycle, the porosity curve of mudstone in the loading process is not coincide with that in the unloading process, the porosity curve in the loading process was located below that in the unloading process, which indicated that the pore structure change is stress path dependent. With the increase of cycle numbers, the total porosity shown an increasing trend, indicating that the damage of mudstone occurred under the cyclic stress load-unload effects. With the increase of porosity, the breakthrough pressure of mudstone decreased with the increase of the cyclic numbers, which may increase the gas leakage risk. The results can provide significant implication for the underground gas storage security evaluation.

Dynamic separation of Xe and Kr by metal-organic framework and covalent-organic materials： a comparison with activated charcoal

We systematically investigate dynamic separation of Xe and Kr at room temperature using four representative porous materials(Cu-BTC, ZIF-8, COP-4 and activated carbon(AC)). Results indicate that among the four materials, Cu-BTC not only shows the highest retention volume per gram(V_g=788 m L g^(-1), which is 1.8 times of activated carbon(436 m L g^(-1))) under flowing condition, but also can separate 350 ppm Xe from 35 ppm Kr mixture in air with a high Xe/Kr selectivity of 8.6 at room temperature and 200 k Pa, due to its suitable pore morphology, open metal sites, small side pockets in the framework. Moreover, the Cu-BTC also performs well on individual separation of Xe, Kr, CO_2 from five-component gas mixture(Xe:Kr:CO_2:Ar:N_2= 1:1:1:1:0.5, V/V) and has the longest retention time for Xe(20 min) in gas chromatographic separation, suggesting that it is a good candidate for potential applications as polymeric sieves.

Tunable Cage-Based Three- Dimensional Covalent Organic Frameworks

It is extremely challenging to construct three-dimensional(3D)crystalline covalent organic frameworks(COFs)with flexible building blocks and to further explore their tunable or adaptive characteristics due to crystallization and structure determination difficulties.Herein,we constructed three crystalline isostructural 3D-OC-COFs based on a newly synthesized flexible organic cage(6NH_(2)-OC.4HCl)through a novel in situ acid–base neutralization strategy.